Camshaft adjusters are used in combustion engines to vary the timing of the combustion chamber valves in order to be able to structure variably the phase relationship between a crankshaft and a camshaft in a defined angular range between a maximum advanced and a maximum retarded position. The adjustment of the cam timing to the actual load and rotation speed reduces the fuel consumption and emissions. To this end camshaft adjusters are integrated in a drive train, via which a torque is transmitted from the crankshaft to the camshaft. This drive train can be formed for example as a belt, chain or gear drive system.
In a hydraulic camshaft adjuster, the output element and the drive element form one or more pairs of pressure chambers acting against each other, which can be pressurized with hydraulic fluid. The drive element and the output element are arranged coaxially. The filling and evacuation of individual pressure chambers generates a relative movement between the drive element and the output element. A spring acting rotationally between the drive element and the output element presses the drive element in one direction versus the output element in a desired direction. This desired direction can be the same as or opposite to the rotation direction.
One type of hydraulic camshaft adjuster is the vane adjuster. The vane adjuster has a stator, a rotor and a drive wheel with external toothing. The rotor as output element is usually formed connectable in a rotationally fixed manner with the camshaft. The drive element contains the stator and the drive wheel. The stator and the drive wheel are connected together rotationally fixed or alternatively are formed as one piece with each other. The rotor is arranged coaxial to the stator and inside the stator. The rotor and the stator, with their radially extending vanes, form oil chambers with opposing action which can be subjected to oil pressure and enable a relative rotation between the stator and the rotor. The vanes are either formed as one piece with the rotor or stator or are arranged as “push-fit vanes” in grooves of the rotor or stator provided for this. Furthermore vane adjusters have various sealing covers. The stator and the sealing covers are fastened together via several screw connections.
Another design of hydraulic camshaft adjuster is the axial piston adjuster. Here via oil pressure a slider element is displaced axially and via helical toothing generates a relative rotation between a drive element and an output element.
U.S. Pat. No. 6,443,112 B1 shows a camshaft adjuster with a locking mechanism, comprising a locking piston and a locking spring, which can fix the output element to the drive element in a middle position or in the maximum retarded position.